The problems of shared syringes are notorious. The practice of sharing syringes without adequate sterilisation between successive users is a major contributor to the transfer of Human Immunodeficiency Virus and Hepatitis with subsequent severe repercussions for the sufferer of such diseases and at a high cost to society of supporting and providing medical attention to those sufferers.
A lesser but still significant risk associated with unclean needles and syringes arises from the possibility of inadvertent needle-stick injuries. This is particularly a problem for law enforcement officers and paramedics who often encounter users of illegal drugs in their professional activities. Additionally, the habits of illegal drug users are such that dangerous by-products of their activities, such as discarded syringes, are often left in places of public access presenting a risk to the users of areas such as public parks and school grounds.
International Publication WO 01/80930 describes a single-use retractable syringe that is highly effective in preventing syringe re-use by ensuring full depression of the plunger during fluid delivery and by ensuring permanent withdrawal of the needle by the plunger back into the syringe barrel. In particular, retractable syringes such as described in International Publication WO 01/80930, Australian Patent 731159 and U.S. Pat. No. 6,083,199 employ a spring to facilitate needle retraction and thereby prevent syringe re-use.
However, resistance by the spring during plunger depression provides an undesirable “feel” to some syringe users, such as intravenous drug users.